The use of aluminum by the automotive industry could achieve over 30% weight savings in vehicle body, chassis and closure components when replacing steel parts. An aluminum intensive vehicle is an efficient way to reduce weight and thus improve fuel economy.
The sub-frame or engine cradle is an assembly with high potential for weight saving due to its size and weight. Conventional sub-frames are made of stamped steel parts. Some high performance automobiles utilize aluminum sub-frames made of aluminum castings or combinations of aluminum castings and extrusions. An aluminum sub-frame made by only extrusions is more attractive to automotive manufacturers since extrusion dies are more affordable compared to casting dies.
It is challenging to design a perimeter type sub-frame with only extrusions to achieve stiffness, performance and weight savings due to the architecture of the sub-frame and the manufacturing constraints of extrusions. More specifically, a perimeter type sub-frame is constructed with a front cross member, a rear cross member and two side rails. The most efficient stiffness design of the side rail should have a closed cross section or partially closed sections at critical locations that will benefit both bending and torsion resistances. Unfortunately, the package space of a sub-frame generally will not allow a straight side rail with a sufficient cross section size, thereby limiting the use of extruded tubes. Thus, in the past, package feasible side rail components have been made by either lateral direction or vertical direction extrusions which have two open surfaces.
This document relates to a new and improved motor vehicle sub-frame, a side rail for that sub-frame and a cross member for that sub-frame. Design challenges are overcome by providing an all extruded aluminum perimeter sub-frame that meets or exceeds strength, bending resistance and torsion resistance requirements while providing substantial weight savings for increased fuel economy. Thus, the motor vehicle sub-frame disclosed herein represents a significant advance in the art.